There are a wide number of applications where it is desirable to remove anionic (negatively charged) species or chemicals from whole blood. For example, anionic exchange materials--supports that have cationic or positively charged surfaces--have been suggested for the removal of barbiturates in drug overdose cases, bilirubin from jaundiced patients and heparin for the prevention of post-operative bleeding. See, e.g., Cipoletti et al., Resin Technology in Medicine in Sorbents and Their Clinical Applications, Giordano ed., Academic Press, New York, 1980; Sideman et al., Contr. Nephrol. (1982) 29:90-100; U.S. Pat. No. 4,800,016 of Yang; Matsuda et al., Art Organs (1989) 13:504-7; Hou et al., Art Organs, (1990) Z4:436-442.
Supported cationic surfaces have also been suggested for the removal of coagulation factors at polymer surfaces for reduced thrombogenicity and improved biocompatibility. See, Wilson, Drug Dev. Res., (1990) 21:79-92.
Despite the promise of such techniques, the use of anionic exchange materials in whole blood applications has been limited by the biocompatibility of the materials used. With the materials used to date, all researchers have noticed a demonstrable removal of platelets--and to a lesser extent white blood cells--from the whole blood samples passed over anion exchange supports. Previous attempts have been made to coat or shield the cation on the surface of the support materials in order to prevent the removal of blood components while retaining the ability to associate with anionic species in the whole blood sample. Such attempts have led to reductions in efficiency and/or capacity to remove anionic species from the whole blood. This is especially true where the anionic species that are being removed from the blood are relatively large (heparin, coagulation factors, etc.).
U.S. patent application Ser. No. 07/562,009, now U.S. Pat. No. 5,474,772 is commonly assigned with the present application. In the '009 Application, a method of medical treatment is described wherein a medical agent is administered to a patient and, after a period of time, the medical agent is removed extracorporeally by passing body fluid over a support adopted to immobilize the agent. Several embodiments of the present invention are adaptable for use in the method described in the '009 Application due to the biocompatibility of the anion exchange materials disclosed herein.
In one such embodiment, and in variations thereof, it is desirable to remove heparin from whole blood. Extracorporeal circulation of blood--required in many surgical and medical procedures--requires the use of systemic heparin to prevent coagulation. Heparin is a highly negatively charged compound. In almost all cases it is necessary to neutralize or remove the heparin in the patient's blood prior to the completion of the surgical procedure. This is required to prevent post-operative bleeding complications. The most commonly used means for neutralizing heparin in this situation is by treatment with protamine sulfate. Unfortunately, the administration of protamine sulfate has several adverse side effects.
Other efforts to remove heparin from whole blood have been investigated. For example, U.S. Pat. No. 4,373,023 of Langer describes a support on which heparinase, an enzyme that degrades heparin, has been immobilized. Others have attempted to use supported or immobilized protamine for heparin removal. See U.S. Pat. No. 4,800,016 of Yang; and Hou et al., Art Organs., (1990) 14:436-442.
Affinity or ion exchange chromatography allows purification or separation of most chemicals based on the molecule's biological function or chemical structure. The separation process occurs because of variations in affinity between the individual members of a mixture of components to a ligand or reactive group which is immobilized on an insoluble support or substrate. The substrates used in affinity chromatography generally are openly porous, have large surface areas, and contain some functionality that can be easily modified for the introduction of ligands. See, for example, Dean & Johnson, Affinity Chromatography: a Practical Approach, IRL Press, Oxford, 1985. The support materials preferably are strong, relatively heat-insensitive, and do not grow or "swell" significantly when in solution.
A common substrate or support is agarose beads, which possess a high degree of surface hydroxyl groups (--OH). The hydroxyl group is ideal for support materials due to its ability to be easily converted to other reactive functionalities such as aldehydes, or to be directly reacted with desired ligands. Ion exchange materials configured as flat, flexible sheets have found widespread use as support materials due to their physical characteristics and ease of use. See, for example, U.S. Pat. No. 4,663,163 of Hou. The sheet supports are commercially available with a variety of reactive groups such as hydroxyl, amine or aldehyde functionalities.
Efforts to make affinity or chromatographic materials biocompatible have been made in the past. Akizawa, T. et al. (1989), Abstracts ASAIO, discloses the use of a cellulose membrane having polyethylene glycol grafted thereon to suppress blood membrane surface interactions. The use of polyethylene oxide moieties on the surface of the materials to increase biocompatibility to surfaces for certain purposes has been described. See, U.S. Pat. Nos. 4,424,311 of Nagoaka et al.; 4,678,468 of Hiroyoshi; and Han, D. K. et al., "Preparation and surface characterization of PEO-grafted and heparin-immobilized polyurethenes," J. Biomed. Meths. Res. (1989) 23:87-104. It has been shown that the ability to confer biocompatibility is proportional to the chain length of the polymer units attached to the surface of the support. See, e.g., Mori et al., Trans Am. Soc. Artif. Intern. Organs, (1982) 28:459-463; Andvade et al., Trans Am. Soc. Artif. Intern. Organs, (1987) 33:75-84.
In a further reference, a heparin/hydrogel coating was described as a method of improving the biocompatibility of activated carbon for hemoperfusion. See, U.S. Pat. No. 4,048,064 of Clark. Macroreticular resin material or coated activated charcoal may also be used in the disclosed process and produce biocompatible hemoperfusion materials.
Other researchers have used quaternary ammonium chemicals to ionically bind an antithrombic agent to a surface. In U.S. Pat. No. 4,678,660 of McGary et al., heparin was complexed with the quaternary compound tridodecyl methyl ammonium chloride and incorporated into polyurethane. In U.S. Pat. No. 4,690,973 of Noishiki et al., glycidyl trimethyl ammoniumchloride (GTMAC) was reacted with collagen, and heparin was immobilized on the surface.
Despite the desirability of obtaining biocompatible anion exchange materials, the prior art does not describe any attempt to include immobilized cationic species and polyethylene oxides in such a way as to obtain the materials disclosed herein. The positive charge required for removal of negatively charged materials such as heparin also removes blood components such as platelets. It was therefore surprising to find that an anion exchange material could be made which would remove heparin without removing significant amounts of platelets or other necessary blood components.
All publications and patents referred to herein are incorporated by reference in their entirety.